Prophecy VS phpunit-injector

Prophecy is a framework for creating test doubles that was initially built for the requirements of phpspec, but it can be used with any other PHP testing framework. Since PHPUnit 4.5 it bundles Prophecy within PHPUnit itself, but as of PHPUnit 9.x this bundling is deprecated and set to be removed in PHPUnit 10.

Recently I have been working a lot with PSR-15 and PSR-18 and one of the characteristics of these recommendations is that it uses the immutable objects specified in PSR-7. Soon after we introduced PSR-18 in our codebase a colleague implemented a client including a unit test that was passing. And yet the code was failing when run in the browser. The cause of this was that the fact that RequestInterface objects are immutable by specification was overlooked. Due to the use of Prophecy and prophesized objects we were struggling to properly test it. Until another colleague introduced me to Argument::that() that is.

This unit test will fail when ran against the implementation from earlier. And in this situation a failing test is a good thing. But for this specific situation another "issue" has made it's way into the testcase; the unit test is now depending on the implementation that is being used for PSR-7. When working in a large codebase - like I currently am - one might have more than just a few usages of these interfaces and thus unit tests. Using the suggested approach, instantiating value objects instead of prophesizing, will lead to a large amount of object instantiations. And this will make switching to another implementation more work. Ideally this instantiating is centralized as much as possible. This is exactly why PSR-17 - HTTP Factories - was introduced. Typically dependencies - like these factories - are injected. For unit tests this is not feasible without plugins. My solution is a bit less fancy; a trait: